Ultraviolet ray generator



July 20, 1948. c. PORTER ETAL 1 2,445,692

ULTRAVIOLET RAY GENERATOR Filed Oct. 11, 1945 INVENTORS: LAWRENCE C.PORTER, HERMAN C. FROELICH,

THEIR AT TORNEY.

Patented July 20, 1948 UNITED STATES PATENT OFFICE ULTRAVIOLET RAYGENERATOR New York Application October 11, 1945, Serial No. 621,732

2 Claims. (Cl. 176-122) Our invention relates generally to ultravioletray generators, and it is an object of our invention to provide anefficient source of ultraviolet radiations of two kinds. Moreparticularly, it is an object of our invention to provide such a devicewhich will produce a large quantity of so-called germicidal" radiationsof short ultraviolet wave length along with a high quantity oferythemal" or health rays" of middle ultraviolet wave length, therebyproviding one device which will serve the double purpose of destroyinggerms and bacteria to prevent diseases as well as furnishing the healthpromoting erythemal radiations also referred to as vitamin D producingradiations.

Another pbject is to provide a device which will produce both germicidaland erythemal radiations in any desired ratio or proportion at highefllciencies.

Another object is to produce such radiations from a gaseous electricdischarge device operating at low temperatures in the neighborhood ofhuman body temperature. v

Further objects and advantages of our invention will appear from thefollowing description of a species thereof.

The drawing is a perspective view of a device comprising our invention.

Referring to the drawing, the device comprises an elongated tubularenvelope I which is made of special ultraviolet transmitting glasscapable of transmitting the short ultraviolet radiations including the2537 A. resonance radiations of mercury vapor. A suitable glass for thispurpose is a borosilicate glass known as No. 9741 manufactured and soldby the Coming Glass Works of Coming, New York. The device otherwiseresembles a conventional commercial fluorescent lamp. At each end of theenvelope i there is an electrode 2 preferably of the activatedthermionic type comprising a coiled coil of tungsten wire coated with asuitable electron emissive material such as alkaline earth oxide. Theelectrodes are connected at their ends to leading-in wires 3 whichextend through the usual glass stems l sealed to the ends of theenvelope l. The envelope contains a small quantity of mercury 5 and asuitable gas, such as argon at a low pressure, for example about 5 mm.The device may be operated from any suitable source of potential at alow current density so correlated to the surface area of the envelopethat it will maintain a positive column discharge between the electrodes2 at a suitably low temperature and corresponding low pressure of themercury vapor for producing a large quantity of radiations of 2537 A.The operating temperature range of the device is preferably about 100 to120 F., with a mercury vapor pressure of the order of microns, althoughthis range may be varied somewhat. Under these conditions a 5 very highproportion (over 90%, for example) of the generated ultraviolet isconcentrated at the 2537 A. line.

The device may be operated from a source of potential 6, 6, such as theordinary 110 volt 60 10 cycle line, in series with a choke coil 1suitably proportioned to properly limit the current. We have illustrateda conventional fluorescent lamp circuit including a switch 8 connectingthe electrodes 2 in series for starting the device, the said switchbeing first closed to connect the electrodes 2 in series across the linefor preheating and then opened to cause the discharge to start.

The interior of the envelope l is provided with a coating 9 offluorescent material or phosphor go which is capable of emcientlytransforming radiations of 2537 A, wave length generated by the idischarge into middle ultraviolet radiations in the erythemal range ofabout 2800 to 3200 A. One phosphor having those characteristics andwhich we at present prefer is the thallium-activated calciumorthophosphate disclosed and claimed in the copending application ofWillard A, Roberts, Serial No. 488,885, filed May 28, 1943, and in thecopending application of H. C. Froelich, Serial No. 608,487, filedAugust 2, 1945. The phosphor coating 9 is applied in such manner that itwill not absorb and transform all the radiations of 2537 A. emitted bythe discharge, but will permit a large proportion of those radiations tobe transmitted through the envelope 1 without transformation orconversion. Although this effect may be produced by coating only part ofthe envelope I with a normal thickness of the powdered phosphor 9, weprefer to coat the entire internal surface of the envelope I with anabnormally thin coating which will absorb and transform some of theradiations emitted by the discharge but will permit a large quantity ofthose radiations to pass through the envelope without 48 transformation.By varying the thickness of the coating or by varying the area of theenvelope coated, or both, we may obtain any desired ratio of germicidaland erythemal radiations from the device, with a preponderance of eithertype of 50 radiation. We have found it desirable at the present time,for such applications as the irradiation of poultry, to proportion thecoating in such manner that of the germicidal and erythemal ultravioletradiations emitted exteriorly of the lamp, about to per cent are theshort radiations of 2537 A. wave length, and about 40 to per cent are inthe middle ultraviolet range of 2800 to 3200 A. The preferred proportionis about 75 per cent germicidal and 25 per cent erythemal ultraviolet.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. An ultraviolet ray generator comprising a gaseous electric dischargedevice of the low pressure mercury vapor type which during operationemits a preponderance of germicidal ultraviolet radiations of 2537 A.wavelength, said device comprising an envelope of material pervious toultraviolet radiations including those of 2537 A. wavelength, and acoating on said envelope of fluorescent material consisting ofthallium-activated calcium phosphate which is capable of convertingradiations of 2537 A. wavelength to ultraviolet radiations of longerwavelength including the erythemal range of about 2800 to 3200 A.wavelength, the said coating being proportioned in such relation to thearea of the envelope that the said germicidal and erythemal radiationsare emitted externally of the device in the ratio of about 60 to 90%germicidal and 40 to 10% erythemal radiations.

2. An ultraviolet ray generator comprising a gaseous electric dischargedevice of the low pressure mercury vapor type which during operationemits a preponderance of germicidal ultraviolet radiations of 2537 A.wavelength, said device comprising an envelope of material pervious toultraviolet radiations including those of 2537 A. wavelength, and acoating on said envelope of fluorescent material consisting ofthallium-activated calcium phosphate which is capable of convertingradiations of 2537 A. wavelength to ultraviolet radiations of longerwavelength including the erythemal range of about 2800 to 3200 A.wavelength, the said coating being proportioned in such relation to thearea of the envelope-that the said germicidal and erythemal radiationsare emitted externally of the device in the ratio of about germicidaland 25% erythemal radiations.

LAWRENCE C. PORTER. HERMAN C. FROELICH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,234,254 Hull Mar. 11, 19412,272,992 Hebo Feb. 10, 1942 2,347,307 Whitman Apr. 25, 1944 2,355,258Biggs Aug. 8, 1944 2,362,384 Libby Nov. 7, 1945 2,362,385 Libby Nov. 7,1945 FOREIGN PATENTS Number Country Date 387,130 Great Britain Feb. 2,1933 535,000 Great'Britain Mar. 25, 1941

